Single Neutrons Research Articles

OBTAINING NEUTRON MATTER AND HYPERHEAVY NUCLEI: POSSIBLE QUANTUM-TECHNOLOGICAL INSTRUMENTAL APPROACHES

Possible mechanisms of creation of both hyperheavy nuclei by electron-nuclear collapse and neutron matter by condensation of ultracold neutrons are discussed. The fundamental possibility of the existence of such objects was previously substantiated by A.B.Migdal, who suggested that the known set of proton-neutron nuclei with mass numbers from 0 to 300 and a maximum specific binding energy of about 8 MeV / nucleon at A≈60 corresponds to the first region, beyond which (starting from about the charge Z≈ ( hc/e2 )3/2 ≈1600 ) there is an additional region describing a possible state of nuclear matter, stabilized by a pion condensate. In this region, the maximum specific energy corresponds to ≈15 MeV / nucleon at A ≈ 100000. It is shown that neutron matter can be obtained under certain conditions, and its systematization can be realized as an addition to the Periodic Table. When solving such problems, it becomes quite real to study not only physical, but also chemical, and possibly engineering and technical properties. Analysis shows that the stability of neutron matter at the microlevel is ensured by the Tamm interaction and the Hund beta equilibrium. Such matter can be quite stable not only on the mega-level (neutron stars) due to gravitational interaction, as was a priori assumed earlier, but also on the scale of "ordinary" matter. The process of neutronization is possible not only with critical gravitational interaction, but also by other mechanisms (supercritical increase in the atomic number of elements due to electron-nuclear collapse and condensation of ultracold neutrons), which opens the way to the fundamental possibility of obtaining both neutron matter in laboratory conditions and superheavy nuclei. Based on the works of Migdal, Tamm and Hund, the possibility of the existence of stable neutron matter (with Z >> 175, N >> Z, A> 10 3 -10 5 and a size of 200-300 femtometers and more) is argued at the microlevel, and not only at the mega-level, as is now considered in astrophysics. A critical analysis of the well-established concept of the minimum possible mass of neutron stars is carried out. The following quantum technological approaches to the realization of UCN condensation are proposed: 1. Slow isothermal compression; 2. Refrigerator for dissolving helium-3 and helium-4; 3. Use of a conical concentrator for UCN focusing (Vysotskii cone); 4. Magnetic trap; 5. Additional UCN laser cooling. Neutron matter is considered as a potential cosmological candidate for dark matter. One should take into account the possibility of the formation of fragments of neutron matter as dark matter (neutral, femto-, pico- and nanoscale, the cooling of relics makes it difficult to detect them by now) already at the initial origin of the Universe, which is the dominant process. The observable part of the Universe is formed by the residual part of protons, and then by decayed single neutrons and unstable fragments of neutron matter (with Z> 175, N >> Z, but A <10 3 -10 5 ).

Unfolding simulation of single-energy and continuous fast neutrons spectrum based on micro-pattern gas detector

This paper focuses on the feasibility of fast neutron energy spectrum measurement. The MCNPX and Geant4 are used to simulate two conversion models of stacking neutrons to protons in the triple GEM cathode coupled with multilayer polyethylene, with five kinds of single-energy neutron sources and Am-Be continuous neutron sources taken as research objects. The response function to 160 single energy neutrons and the recoil proton spectrum distribution of the above sources of the detection system are obtained by simulation. Using GRAVEL algorithm and MLEM algorithm and through simulation, the recoil proton spectra of six kinds of fast neutron sources are obtained, and they are further analyzed. The spectrum outcome is compared with the standard input spectrum, showing that they are in good agreement with each other. The relative uncertainty of the unfolding spectrum is around 10%–15%. In this part the relation of gas detector with the precision of unfolding spectrum is also discussed. The result shows that when the energy resolution of micro-pattern gas detection is better than 30%, the accuracy of fast neutron spectrum can meet the needs of practical applications. Furthermore, a new transformation model is proposed based on previous experiments and proves the feasibility of applying micro-pattern gas detector to fast neutron detection of simulation. Moreover, spectrum reconstruction can be achieved by using the obtained recoil proton spectrum combined with a suitable inversion algorithm. The modeling and spectrum analysis of this study can provide a different method of applying the fast neutron detection system composed of micro-pattern gas detectors to the detection of unknown fast neutron sources and also to the source recognition through spectrum reconstruction.

On Heating and Relaxation of the Electron—Hole-Gas Energy in the Track of a Primary Recoil Atom

On the basis of the Monte Carlo algorithm, a method for calculating the energy spectrum of hot nonequilibrium electrons and holes in the track of a primary recoil atom after being exposed to single fast neutrons is developed. The heating and subsequent relaxation of nonequilibrium charge carriers in silicon in the track of a charged particle with initial energies in the range of 50–200 keV are calculated. The characteristic temperatures of the electron and hole plasma are obtained, which amount to 5400 and 2700 K, respectively. The effect of the radiation-induced heating of charge carriers on the failure stability of static memory cells is discussed.

Разогрев и релаксация энергии электронно-дырочного газа в треке первичного атома отдачи

Based on the Monte Carlo algorithm, a method has been developed for calculating the energy spectrum of hot nonequilibrium electrons and holes in the track of the primary recoil atom when exposed to single fast neutrons. The calculations of the heating and subsequent relaxation of nonequilibrium charge carriers in silicon in the track of a charged particle with initial energies in the range of 50...200 keV are carried out. The characteristic temperatures of the electron and hole plasma were obtained, which amounted to 5400 K and 2700 K, respectively. The effect of radiation-induced heating of charge carriers on the failure stability of static memory elements is discussed.

Photocurrent From Single Collision 14-MeV Neutrons in GaN and GaAs

Accurate predictions of device performance in 14-MeV neutron environments rely upon understanding the recoil cascades that may be produced. Recoils from 14-MeV neutrons impinging on both gallium nitride (GaN) and gallium arsenide (GaAs) devices were modeled and compared to the recoil spectra of devices exposed to 14-MeV neutrons. Recoil spectra were generated using nuclear reaction modeling programs and converted into an ionizing energy loss (IEL) spectrum. We measured the recoil IEL spectra by capturing the photocurrent pulses produced by single neutron interactions with the device. Good agreement, with a factor of two, was found between the model and the experiment under strongly depleted conditions. However, this range of agreement between the model and the experiment decreased significantly when the bias was removed, indicating partial energy deposition due to cascades that escape the active volume of the device not captured by the model. Consistent event rates across multiple detectors confirm the reliability of our neutron recoil detection method.

Neutron-neutron angular and energy-angle correlations of plutonium samples with varying α-ratio

Abstract Accurate and timely characterization of physical properties pertinent to plutonium bearing materials is important for fulfilling nuclear nonproliferation and safeguards goals. Physical properties include the fissile mass, leakage multiplication, and the α -ratio, defined as the ratio of ( α ,n) neutrons to spontaneous fission neutrons. Traditionally, these properties can be inferred by relating the measured neutron multiplicity count rates to the well-established point kinetics moments equations; the current state-of-the-art utilizes 3 He-based detection systems. Organic scintillators have been used extensively to study and measure characteristic signatures in the neutron angular and energy distributions. Previous work has proposed techniques that independently leverage the energy and angle sensitivity of organic scintillators to estimate the α -ratio of plutonium bearing material; however, it is expected that the energy and angular distributions are correlated to one another due to the underlying physics of fission and ( α ,n) neutron emissions. This work presents experimental results that characterize neutron-neutron angular distribution and subsequently the neutron-neutron energy-angle correlations for plutonium samples of similar mass and multiplication, but varying α -ratio due to the type of low-Z impurity. Full neutron-neutron angular distributions are presented using a low-energy detection threshold of 0.10, 0.15, and 0.20 MeVee (0.73, 0.96, 1.16 MeV neutron-equivalent energy). Neutron anisotropy was quantified by taking the ratio of neutron-neutron coincidences at 180°to those at 90°, where a value of unity indicates a purely isotropic source. The results show that the observed neutron-neutron correlations transition away from fission-induced signal to the cross-talk signal associated with single ( α ,n) neutrons with increasing α -ratio. Energy-angle correlations are characterized by calculating the neutron anisotropy at various detection thresholds and show positive correlation between the observed anisotropy and the energy of the neutrons.

Optical identification and quantification of single neutron detection in 6LiF/ZnS scintillators using a CMOS camera

The possibility of observing the light from single neutron detection in scintillation materials by highly pixelated silicon sensors coupled with a demagnification optical lens could lead to a new generation of position-sensitive neutron detectors with relatively large area coverage and competitive spatial resolution. Several ZnS/6LiF-based scintillators were tested at the SINQ Beamline for Neutron Optics (BOA) using a neutron radiography setup mounting a sCMOS camera with an f/0.95 commercial objective. Single neutrons were identified and distinguished from the camera noise and particles detected directly in the silicon sensor in all the tested scintillators, with exposures starting from 1 ms. Linearity between neutron counting and exposure times was obtained from 10 ms up to 200 ms.

Optical Observation of Single Neutron Detection

The feasibility of using highly pixelated light sensors as neutron detectors is the subject of a collaboration between ILL and ESS Bilbao. The fast paced development of camera sensors can meet the future challenges of neutron detection if an optical coupling able to increase the signal to noise ratio and enlarge the detection area is identified. Fiber optics tapers seem the best candidates, but issues about their radiation resistance and price make photographic objectives a more sensible choice. The performances of photographic optics have been tested as well as the light output of several thermal neutron scintillators. Thanks to the use of a highly transmissive optics, single neutrons could be observed in 6LiF/ZnS(Ag) for the first time.

Study of bound states in 10Be by one neutron removal reactions of 11Be

The bound states of 10Be have been studied by removing single neutrons from 11Be nuclei. A 2.8 MeV u–1 beam of 11Be was produced at ISOLDE, CERN and directed on to both proton and deuteron targets inducing one-neutron removal reactions. Charged particles were detected to identify the two reaction channels (d, t) and (p, d), and the individual states in 10Be were identified by gamma detection. All bound states but one were populated and identified in the (d, t) reaction. The combination of REX-ISOLDE and MINIBALL allowed for a clean separation of the high-lying states in 10Be. This is the first time these states have been separated in a reaction experiment. Differential cross sections have been calculated for all the reaction channels and compared to DWBA calculations. Spectroscopic factors are derived and compared to values from the litterature. While the overall agreement between the spectrocopic factors is poor, the ratio between the ground state and the first excited state is in agreement with the previous measured ones. Furthermore, a significant population of the state is observed, which which may indicate the presence of multi-step processes at our beam energy.

Participant and spectator scaling of spectator fragments in Au + Au and Cu + Cu collisions atsNN=19.6and 22.4 GeV

Spectator fragments resulting from relativistic heavy ion collisions, consisting of single protons and neutrons along with groups of stable nuclear fragments up to Nitrogen (Z=7), are measured in PHOBOS. These fragments are observed in Au+Au (sqrt(sNN)=19.6 GeV) and Cu+Cu (22.4 GeV) collisions at high pseudorapidity ($\eta$). The dominant multiply-charged fragment is the tightly bound Helium ($\alpha$), with Lithium, Beryllium, and Boron all clearly seen as a function of collision centrality and pseudorapidity. We observe that in Cu+Cu collisions, it becomes much more favorable for the $\alpha$ fragments to be released than Lithium. The yields of fragments approximately scale with the number of spectator nucleons, independent of the colliding ion. The shapes of the pseudorapidity distributions of fragments indicate that the average deflection of the fragments away from the beam direction increases for more central collisions. A detailed comparison of the shapes for $\alpha$ and Lithium fragments indicates that the centrality dependence of the deflections favors a scaling with the number of participants in the collision.

Development of a high-speed camera system for neutron imaging at a pulsed neutron source

A neutron energy resolved imaging system with a time-of-flight technique has been newly developed and installed at Japan Proton Accelerator Research Complex (J-PARC) with the aim to investigate more preciously and rapidly a spatial distribution of several elements and crystals in various kinds of materials or substances. A high-speed video camera (CMOS, 1300k frame/s) equipped system allows to obtain TOF images consecutively resolved into narrow energy ranges with a single pulsed neutrons while conventional CCD camera imaging system could obtain only one TOF image in an arbitral neutron energy region in the pulsed neutron energy region from 0.01eV to a few keV. Qualities of the images obtained with the system, such as spatial resolution (defined by modulation transfer function, 0.8 line-pairs/mm at En∼0.01eV), dependence of the brightness on the neutron energy and measurement errors (∼2%) of the system were examined experimentally and evaluated by comparison with those of conventional imaging system. The results obtained in the experiments show that the system can visualize the neutron energy resolved images within a small error even at high speed.

AN INTERPLAY BETWEEN NONLOCALITY AND QUANTUM VIOLATION OF PATH–SPIN NONCONTEXTUALITY

In terms of a suitable variant of the EPR–Bohm example, we argue that the quantum mechanically predicted and experimentally verified violation of a Bell-type path–spin noncontextual realist inequality for an "intraparticle" path–spin entanglement involving single neutrons can be used to infer a form of nonlocality, distinct from Bell-type nonlocality, that is required for any relevant hidden variable model to be compatible with the quantum mechanical treatment of an EPR–Bohm-type "interparticle" entanglement.

Energy entanglement in neutron interferometry

Entanglement between degrees of freedom, namely between the spin, path and (total) energy degrees of freedom, for single neutrons is exploited. We implemented a triply entangled Greenberger–Horne–Zeilinger(GHZ)-like state and coherently manipulated relative phases of two-level quantum subsystems. An inequality derived by Mermin was applied to analyze the generated GHZ-like state: we determined the four expectation values and finally obtained M=2.558±0.004≰2. This demonstrates the violation of a Mermin-like inequality for triply entangled GHZ-like state in a single-particle system, which, in turn, exhibits a clear inconsistency between noncontextual assumptions and quantum mechanics and confirms quantum contextuality.

New aspects of geometric phases in experiments with polarized neutrons

Geometric phase phenomena have been observed with single neutrons in polarimeter and interferometer experiments. Interacting with static and time-dependent magnetic fields, the state vectors acquire a geometric phase tied to the evolution within spin subspace. In a polarimeter experiment the non-additivity of quantum phases for mixed spin input states is observed. In a Si perfect-crystal interferometer experiment appearance of geometric phases, induced by interaction with an oscillating magnetic field, is verified. The total system is characterized by an entangled state, consisting of neutron and radiation fields, governed by a Jaynes–Cummings Hamiltonian. In addition, the influence of the geometric phase on a Bell measurement, expressed by the Clauser–Horne–Shimony–Holt (CHSH) inequality, is studied. It is demonstrated that the effect of the geometric phase can be balanced by an appropriate change of Bell angles.

Kochen–Specker theorem studied with neutron interferometer

The Kochen–Specker theorem shows the incompatibility of noncontextual hidden variable theories with quantum mechanics. Quantum contextuality is a more general concept than quantum non-locality which is quite well tested in experiments using Bell inequalities. Within neutron interferometry we performed an experimental test of the Kochen–Specker theorem with an inequality, which identifies quantum contextuality, by using spin-path entanglement of single neutrons. Here entanglement is achieved not between different particles, but between degrees of freedom of a single neutron, i.e., between spin and path degree of freedom. Appropriate combinations of the spin analysis and the position of the phase shifter allow an experimental verification of the violation of an inequality derived from the Kochen–Specker theorem. The observed violation 2.291±0.008≰1 clearly shows that quantum mechanical predictions cannot be reproduced by noncontextual hidden variable theories.

Doubly magic tin

By swapping the roles of the target and beam in an experiment that is otherwise impossible to implement, researchers have confirmed the doubly magic nature of the neutron-rich radioactive tin isotope 132Sn. Atomic nuclei have a shell structure that allows for 'magic' numbers of neutrons and protons, analogous to the noble gases in atomic physics. Knowledge of the properties of single-particle states outside nuclear shell closures in exotic nuclei is important for fundamental understanding of nuclear structure and nucleosynthesis. Using a nucleon transfer technique to add single neutrons to the short-lived tin isotope 132Sn, to create the even-shorter-lived 133Sn, Jones et al. have been able to confirm the closed-shell 'doubly magic' nature of 132Sn. Measurements of the spectrum of quantum states available to the added neutron show that the characteristics of the 133Sn nucleus are determined almost completely by this single neutron. This finding extends the validity of the shell model to neutron-rich nuclei, and provides a benchmark for predicting the properties of nuclei even farther from stability, including those involved in neutron-capture reactions in supernovae.

Testing quantum contextuality with macroscopic superconducting circuits

We propose an experimental procedure to macroscopically test the Kochen-Specker theorem with superconducting qubits. This theorem, which has been experimentally tested with single photons and neutrons, elucidates the conflict between quantum mechanics and noncontextual hidden variable theories. Two Josephson charge qubits can be controllably coupled by using a two-level data bus built with a phase qubit. Then, by performing joint nondestructive quantum measurements of two distinct qubits, we show that the proposed circuits could demonstrate quantum contextuality at a macroscopic level.

Entanglement between degrees of freedom of single neutrons

Non-local correlations between subsystems sufficiently separated in spacetime have been extensively discussed in the light of the Einstein, Podolsky and Rosen (EPR) paradox, together with Bell's inequality. Within quantum terminology, such a non-locality can be interpreted as a consequence of the entanglement of subsystems. A more general concept, i.e., quantum contextuality, compared to non-locality, can be introduced to describe other striking phenomena predicted by quantum theory. As examples of quantum contextuality, we report several neutron interferometer experiments: a violation of a Bell-like inequality, a Kochen–Specker-like phenomenon, a quantum state tomography. Entanglement is achieved not between the particles, but between the degrees of freedom of a single-particle. Furthermore, an experiment dealing with triple entanglement is presented.

Determination of the multiplication of leakage neutrons and the fissile material mass in deeply subcritical systems

The previously developed analysis of measurements of neutron multiplication in deeply subcritical states of multiplying media by the α-Rossi method (method of double neutron-neutron coincidences) is supplemented by a new analysis of triple coincidences. To obtain the neutron multiplication and the effective neutron multiplication coefficient, it is no longer necessary to know the intensity of the source of spontaneous fissions - it is determined from experiments. This makes it possible to determine simultaneously the mass and enrichment of a fissile substance placed in a container. Measurements are performed and analyzed using uranium and plutonium blocks and fast-neutron detectors as well as AWCC (active well coincidence counters) neutron detectors. Previous measurements performed using the coincidence counters are analyzed. It is shown that without calibration of the 240 Pu and 239 Pu mass by measurement of counting rate of single neutrons as well as double and triple coincidences in ordinary experiments the error (1σ) in determining the mass fraction of 240 Pu in plutonium is 0.3-0.8% and the error for all plutonium is 3-12%.

What has a symmetry violation in particle physics to do with non-locality?

Particle physics has become an interesting testing ground for fundamental questions of quantum mechanics (QM). The massive meson-antimeson systems are specially suitable as they offer a unique laboratory to test various aspects of particle physics (\(\cal{CP}\) violation, \(\cal{CPT}\) violation, ...) as well to test the foundations of QM (local realistic theories versus QM, Bell inequalities, decoherence effects, quantum marking and erasure concepts, ...). We focus here on a surprising connection between the violation of a symmetry in particle physics –the \(\mathcal{CP}\) symmetry (\(\cal{C}\)=charge conjugation, \(\cal{P}\)=parity)– and non-locality. This is achieved via Bell inequalities which discriminate between local realistic theories and QM. Further we present a decoherence model which can be tested by accelerator experiments at the DAΦNE (Italy) and at the KEK-B machine (Japan). We show that there is a simple connection between a decoherence parameter and different measures of entanglement, i.e., entanglement of formation and concurrence. In this way the very basic mathematical and theoretical concepts about entanglement can be confronted directly with experiments. Similar decoherence models can also be tested for entangled photon systems and single neutrons in an interferometer.